1. Field of the Invention
The present invention relates, generally, to an antibiotic delivery system and, more specifically, to such a system for treating an infected synovial joint and adjacent medullary canals as a means of eliminating infection during a two-stage re-implantation of an orthopedic prosthesis.
2. Description of the Related Art
A total joint replacement (TJR) is a medical procedure that involves the repair and replacement of joints, such as hips and knees. In these cases, the bones at the hip or knee joints are prepared to receive orthopedic implants that mimic the structure of the joint that is replaced. For example, a total knee replacement is representatively shown at 10 in FIG. 1. The total knee replacement 10 includes tibial 12 and femoral 14 components that imitate the structure and function of the natural knee joint. The tibial component 12 is operatively mounted to the tibia bone 16 and the femoral component 14 is operatively mounted to the femoral bone (not shown). Similarly, a total hip replacement includes a femoral component that terminates in a neck having a hemispherical ball that mimics the upper terminal portion of the natural femoral bone.
Currently, there are approximately one million total joint replacement (TJR) surgeries involving either hips or knees performed annually in the United States. Obviously, more TJR surgeries are performed throughout the world. However, the demand for TJR surgery is expected to soar in the future. Doctor-diagnosed arthritis is expected to increase 40% from 2005 to 2030. According to the 2003 National Institute of Health Census Panel Report on total knee replacement, only 9% to 13% of TJR candidates have been willing to undergo the procedure. As patients become more aware of their options, as well as the success of TJR, demand may reach even higher levels.
Baby boomers will start reaching the age of 65 years in 2011. Also, over the past decade, the prevalence of TJR has increased not only in older patients (those who are 65 years or older) but also in younger patients (those less than 65 years old). Premium implant technology such as hard-on-hard bearings and hip resurfacing have been introduced to address the increased activity and longevity of younger patients. The demand for primary total hip and total knee replacements on patients younger than 65 years old was projected to exceed 50% of joint replacement recipients by 2011 and 2013, respectively. Demand for primary total hip replacement is expected to grow 174% and for total knee replacement by 673% by the year 2030. Data collected from the U.S. Nationwide Implant Sample (NIS) between 1993 and 2005 has also been evaluated. This data indicates that by 2030 future demand of primary and revision TJR procedures (where an older implant is replaced with a new one) will be significant. For example, primary total knee replacements are projected to be 4,580,000. The need to revise and re-implant total knee replacements is projected to be 269,000. Primary total hip replacements are projected to be 975,000. And the need to revise and re-implant total hip replacements is projected to be 103,000 per year. These estimated projections total 6,000,000 TJR surgeries annually.
In relatively rare cases, however, infection is a devastating complication of TJR surgeries. The rate of infection in these types of surgeries ranges between 0.5% and 1.5%. Unless an infection is properly diagnosed within the first two to four weeks following the original surgery (which is uncommon), the infected implant must be removed in combination with an extensive debridement of the surrounding joint tissue and bone. According to the Center for Disease Control, there are currently approximately 12,000 infected TJR cases annually in the United States. Obviously, this number increases when the entire worldwide scope of TJR surgeries is considered. At 1% infection rate, and assuming the projections noted above are generally accurate, there will be 60,000 instances of infected total joints annually in the future.
Over the past two decades, the standard of care for treatment of an infected TJR in the United States has included a two-stage re-implantation process. In the first stage of this process, the infected components are surgically exposed by incision. Scar tissue is then de-bulked as well as other soft tissue releases, and sometimes an osteotomy. This stage also includes the removal of all prosthetic components and foreign material including, for example, acrylic bone cement. After extensive joint debridement of infected soft tissue and bone, a spacer block consisting of heavily dosed antibiotic bone cement is placed temporarily into the joint space. The purpose of the antibiotic bone cement is to sterilize the joint environment and to serve as an antibiotic delivery system. Additionally, the bone cement acts as a spacer to preserve joint space and maintains ligament length. However, the antibiotic released by the bone cement is uncontrolled and is quite costly to use. For example, a typical knee spacer may require three bags of acrylic bone cement, twelve vials of an antibiotic such as Tobramycin (1.2 g) at a cost of $800 per vial, and six vials of an antibiotic such as Vancomycin (1 g) at $17 per vial. This quickly adds up to about $11,000 in material alone. In addition, more operating room time is necessary to prepare this spacer material. This increases the cost of the operation.
Under the current standard of care, following the removal of the infected implant and the insertion of the antibiotic bone cement spacer, the patient must generally wait between six and, more typically, twelve weeks before the second stage of the procedure can be performed. This period of time is necessary so that the medical professionals can be confident that the infection has been successfully eradicated. Only after the infectious condition has been eliminated, may the second stage proceed. During the second stage, the new prosthesis is re-implanted. The success rate with this two-stage re-implantation process is typically around 90%.
In other countries, such as throughout Europe, a one-stage re-implantation process has been popular. This involves the removal of the infected implant, as noted above, followed by aggressive debridement and then immediate re-implantation of a new implant. The success rate for this technique has typically been in the 70%-85% range. However, this technique has not gained popularity to any degree in the United States. The one-state implantation process is generally reserved for patients who are considered to be too feeble or sick to undergo the traditional two-stage re-implantation process.
Both the one-stage and two-stage surgical re-implantation protocols have their disadvantages. For example, and as noted above, the two-stage re-implantation process requires six to twelve weeks between operations. This is a very difficult time for the patient as they do not have a functional joint in place and it is typically very painful to mobilize or ambulate with an antibiotic spacer. Articulating spacers are somewhat better than static spacers, but are also more expensive as well as more difficult and time-consuming to place during the original stage one procedure. From a health care standpoint, the two-stage procedure also requires two separate hospitalizations. Finally, from a surgeon's standpoint, a significant amount of scar tissue develops during the time span between the two procedures. This makes for a very difficult and time-consuming second stage operation. In addition, the two-stage re-implantation process involves not one, but two, very difficult surgical procedures. The estimated cost of removing the infected original implant, eliminating the infection, extended hospitalization, nursing home care or home health care during the period between the first and second operations, a well as re-implanting a new prosthesis is currently roughly $100,000 per case. This is a tremendous overall burden on the universal health care system and, in the United States alone, reaches approximately $1.2 billion per year. This statistic does not begin to measure losses in patient economic productivity, quality of life, as well as pain and suffering. Moreover, this statistic does not reflect the costs associated with the projected increase in TJR operations in the future as noted above.
On the other hand, a one-stage re-implantation surgical protocol requires absolute identification of the infecting organism in order to proceed. Unfortunately, it is very difficult to achieve this absolute identification in the current health care systems. In addition, a one-stage re-implantation protocol requires the use of fully-cemented components. Fully-cemented components are typically not favored by U.S. surgeons for revision surgery. Fully-cemented components typically require very high amount of antibiotic. This often is as high as 10% by weight. For example, 4 g of antibiotic are required for a 40 g bag of cement. The increase of antibiotic by weight raises concerns regarding structural weakening of the cement.
Moreover, and in both one-stage and two-stage re-implantation surgical protocols, the release of the antibiotic from the bone cement is completely uncontrolled. This is a significant disadvantage of both protocols and essentially acts to lengthen the time between the first and the second surgical procedures in the two-stage re-implantation process.
Thus, there remains a need in the art for a device that may be employed during re-implantation surgical procedures that may be used to deliver antibiotic in a controlled and titratable manner directly into the synovial joint cavity and adjoining medullary canals as a means of eliminating the infection following the removal of a previous orthopedic implant. In addition, there remains a need in the art for such a device that can provide stability and maintain the physical dimensions of joint space and normal soft tissue envelope in any joint undergoing the re-implantation of an orthopedic implant. In addition, there remains a need in the art for such a device that may be easily employed, facilitates the reduction in the time needed to conduct the stage one re-implantation surgery and that reduces the overall time between the first and second stages of a two-stage re-implantation surgical protocol.